use platform-independent font for gm

Create a custom typeface and scaler to render simple paths the
same on all platforms.

GM tests are modified to explicitly select the custom typeface.

R=reed@google.com, mtklein@google.com, bungeman@google.com
TBR=reed

Author: caryclark@google.com

Review URL: https://codereview.chromium.org/348323003
23 files changed